The application relates to a semiconductor device with a semiconductor body and to a method for its production. The semiconductor body includes drift zones of epitaxially grown semiconductor material of a first conduction type. The semiconductor body further includes charge compensation zones of a second conduction type complementing the first conduction type, which are arranged laterally adjacent to the drift zones. The charge compensation zones are provided with a laterally limited charge compensation zone doping, which is introduced into the epitaxially grown semiconductor material.
A minimum on resistance is desirable in charge compensation devices of this type. In order to achieve a further reduction of this on resistance, the level of drift zone doping material has to be increased further. Owing to the compensation principle, however, the doping of the charge compensation zones has to be increased in the same way. In order to ensure a complete depletion of charge carriers from the drift zones in the off phase of the semiconductor device in spite of such an increase in the level of doping material both in the drift zones and in the charge compensation zones, the geometrical period in the form of the step size of the charge compensation zones and possibly even of the drift zones has to be reduced further at the same time. In other words, the concentration of doping material per unit of area as integrated in the horizontal direction must not be higher than twice the breakdown charge. The term breakdown charge denotes the charge carrier quantity (doping material concentration quantity) per unit of area which, starting from a p-n junction, is depleted if the breakdown field strength is applied. As the compensation regions are depleted from both sides, the requirement that the regions should be capable of being depleted is equivalent to the requirement that the concentration of doping material per unit of area as integrated in the horizontal direction should not be higher than twice the breakdown charge. These conditions have to be met both by the compensation regions and by the drift zones. Similar to the breakdown field strength, the breakdown charge is determined by the concentration of doping material; for silicon is lies between 1×1012 cm−2 at low doping and 3×1012 cm−2 at high doping.
By using trench technology, wherein the charge compensation zones and/or the drift zones are arranged in trench structures, very small step sizes can be obtained in theory, but this technology has not yet penetrated the market, so that the concept of multiple epitaxy is used to build semiconductor devices of this type. In multiple epitaxy, epitaxial growth phases are interspersed with unmasked large-area and masked selective implantation processes for doping materials. To reduce costs, the number of epitaxial growth phases is limited.
The regions of a complementary conduction type for the charge compensation zones, which are introduced by masked or selective ion implantation and typically doped with boron, have to diffuse together through the epitaxial growth phases of finite thickness. This however unavoidably involves major widening of the columns or strips of charge compensation zone material. To reduce this widening problem caused by lateral diffusion, non-doped epitaxial layers can be grown in the epitaxial growth phase, whereupon both doping materials of the first conduction type and doping materials of the complementary second conduction type can be introduced in succession by ion implantation near the surface between individual epitaxial growth phases, so that the widening caused by lateral outdiffusion while the charge compensation zones diffuse together can be noticeably reduced by a relatively high adjacent n-doping of the drift zones.
However, initially high-impedance non-doped epitaxial layers are generated in the epitaxial growth phase, so that the on resistance of the drift zones cannot be reduced as desired. The n-doping in the middle of the epitaxial growth phase is relatively low can only be compensated by raising the general level of implanted doping material in order to reduce the on resistance. A high level of doping material, however, automatically complicates the manufacturing process, as breakdown voltage is highly dependent on wrong doping. The higher the level of doping material, the higher are its fluctuations and the more difficult is it to obtain the required breakdown voltage.
For these and other reasons, there is a need for the present invention.